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Date: Thu, 8 Jul 2021 11:00:39 +0800
From: He Fengqing <hefengqing@...wei.com>
To: Song Liu <song@...nel.org>
CC: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [bpf-next 3/3] bpf: Fix a use after free in bpf_check()
在 2021/7/7 15:25, Song Liu 写道:
> On Tue, Jul 6, 2021 at 8:53 PM He Fengqing <hefengqing@...wei.com> wrote:
>>
>> In bpf_patch_insn_data, env->prog was input parameter of
>> bpf_patch_insn_single function. bpf_patch_insn_single call
>> bpf_prog_realloc to realloc ebpf prog. When we need to malloc new prog,
>> bpf_prog_realloc will free the old prog, in this scenery is the
>> env->prog.
>> Then bpf_patch_insn_data function call adjust_insn_aux_data function, if
>> adjust_insn_aux_data function return error, bpf_patch_insn_data will
>> return NULL.
>> In bpf_check->convert_ctx_accesses->bpf_patch_insn_data call chain, if
>> bpf_patch_insn_data return NULL, env->prog has been freed in
>> bpf_prog_realloc, then bpf_check will use the freed env->prog.
>
> Besides "what is the bug", please also describe "how to fix it". For example,
> add "Fix it by adding a free_old argument to bpf_prog_realloc(), and ...".
> Also, for the subject of 0/3, it is better to say "fix potential
> memory leak and ...".
Thanks for your suggestion.
>
>>
>> Signed-off-by: He Fengqing <hefengqing@...wei.com>
>> ---
>> include/linux/filter.h | 2 +-
>> kernel/bpf/core.c | 9 ++++---
>> kernel/bpf/verifier.c | 53 ++++++++++++++++++++++++++++++++----------
>> net/core/filter.c | 2 +-
>> 4 files changed, 49 insertions(+), 17 deletions(-)
>>
>> diff --git a/include/linux/filter.h b/include/linux/filter.h
>> index f39e008a377d..ec11a5ae92c2 100644
>> --- a/include/linux/filter.h
>> +++ b/include/linux/filter.h
>> @@ -881,7 +881,7 @@ void bpf_prog_jit_attempt_done(struct bpf_prog *prog);
>> struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags);
>> struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flags);
>> struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
>> - gfp_t gfp_extra_flags);
>> + gfp_t gfp_extra_flags, bool free_old);
>> void __bpf_prog_free(struct bpf_prog *fp);
>>
>> static inline void bpf_prog_clone_free(struct bpf_prog *fp)
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 49b0311f48c1..e5616bb1665b 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -218,7 +218,7 @@ void bpf_prog_fill_jited_linfo(struct bpf_prog *prog,
>> }
>>
>> struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
>> - gfp_t gfp_extra_flags)
>> + gfp_t gfp_extra_flags, bool free_old)
>> {
>> gfp_t gfp_flags = GFP_KERNEL_ACCOUNT | __GFP_ZERO | gfp_extra_flags;
>> struct bpf_prog *fp;
>> @@ -238,7 +238,8 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
>> /* We keep fp->aux from fp_old around in the new
>> * reallocated structure.
>> */
>> - bpf_prog_clone_free(fp_old);
>> + if (free_old)
>> + bpf_prog_clone_free(fp_old);
>> }
>>
>> return fp;
>> @@ -456,7 +457,7 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
>> * last page could have large enough tailroom.
>> */
>> prog_adj = bpf_prog_realloc(prog, bpf_prog_size(insn_adj_cnt),
>> - GFP_USER);
>> + GFP_USER, false);
>> if (!prog_adj)
>> return ERR_PTR(-ENOMEM);
>>
>> @@ -1150,6 +1151,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
>> return tmp;
>> }
>>
>> + if (tmp != clone)
>> + bpf_prog_clone_free(clone);
>> clone = tmp;
>> insn_delta = rewritten - 1;
>>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 41109f49b724..e75b933f69e4 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -11855,7 +11855,10 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
>> new_prog = bpf_patch_insn_data(env, adj_idx, patch, patch_len);
>> if (!new_prog)
>> return -ENOMEM;
>> - env->prog = new_prog;
>> + if (new_prog != env->prog) {
>> + bpf_prog_clone_free(env->prog);
>> + env->prog = new_prog;
>> + }
>
> Can we move this check into bpf_patch_insn_data()?
Ok, I will change this in next version.
>
>> insns = new_prog->insnsi;
>> aux = env->insn_aux_data;
>> delta += patch_len - 1;
> [...]
>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index d70187ce851b..8a8d1a3ba5c2 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -1268,7 +1268,7 @@ static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp)
>>
>> /* Expand fp for appending the new filter representation. */
>> old_fp = fp;
>> - fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0);
>> + fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0, true);
>
> Can we add some logic here and not add free_old to bpf_prog_realloc()?
Ok, maybe we can free old_fp here, never in bpf_prog_realloc.
>
> Thanks,
> Song
> .
>
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